Final answer:
The term meaning a goat in estrus is 'estrous.' This term describes the period when the female is fertile and sexually receptive.
Step-by-step explanation:
The term meaning a goat in estrus is b) Estrous. Estrus is the period during which a female animal is sexually receptive, commonly referred to as being in heat. This term is specific to the time when an animal is fertile and is part of the estrous cycle, not to be confused with caprine, which is an adjective relating to goats in general, or capricious, which can mean unpredictable or whimsical behavior but is not related to the reproductive status of goats.